With the development of display technologies and requirement of better display effect, 3D display technology has attracted broad attention. The hypostasis of 3D display is to produce a stereoscopic effect by a binocular parallax, i.e., a left-eye picture is seen by the left eye of a person, and a right-eye picture is seen by his/her right eye. When the left-eye and right-eye pictures become a pair of stereoscopic images having the parallax, both of these two images will be combined in the brain to generate the 3D effect.
In the prior 3D technology, birefringence grating 3D technology is particularly desirable, because it has an advantage of high brightness and can be used to achieve a 2D/3D switch. As shown in FIGS. 1a-1b, a birefringence grating display device comprises: a display unit 1, a switching device 2 and a birefringence grating 3. The display unit 1 may be a display device, such as a liquid crystal display, an electroluminescence device (EL), or a plasma display panel (PDP). In the display device such as EL and PDP, a polarizing device by which light emitted from the display can be converted into polarized light should be added to the display device. The switching device 2 comprises: an upper substrate, a lower substrate, a first alignment layer and an upper electrode formed on the upper substrate, a second alignment layer and a lower electrode formed on the lower substrate, and liquid crystal molecules encapsulated between the first alignment layer and the second alignment layer. Through the switching device, the light emitted from the display unit 1 can be rotated by 90° or be transmitted without any rotation. As shown in FIGS. 2a-2c, the birefringence grating comprises: a concave grating 3-1 (that can be a concave lens array including a plurality of concave lenses), a substrate 3-2 assembled with the concave grating 3-1 (the alignment layer is formed on a surface of the substrate 3-2), a plurality of aligned and cured liquid crystal molecules 3-3 filled between the concave grating 3-1 and the substrate 3-2. The refractive index of the liquid crystal molecules along a short axis is matched with the refractive index of the concave grating 3-1, such that when the light emitted from the switching device 2 is transmitted through the concave grating 3-1 and the substrate 3-2 in a polarizing direction vertical to a drawing sheet, the light will not be deflected because the two structure have the same refractive index. In this case, the display device presents a 2D display mode (as shown in FIG. 1b). The refractive index of the liquid crystal molecules 3-3 along a long axis is different from the refractive index of the concave grating 3-1. When the light emitted from the switching device 2 is transmitted through the concave grating 3-1 and the substrate 3-2 in a horizontal direction, due to the difference between the refractive index of the liquid crystal molecules 3-3 and that of the concave grating 3-1, the direction of emission light can be deflected like passing through a convex lens, and the display effect as achieved by combined lens can be obtained. In this case, the display device presents a 3D display mode (as shown in FIG. 1a).
The traditional method of manufacturing the birefringence grating comprises following steps: firstly, forming a concave grating and performing a rubbing alignment, or forming a concave grating, coating an alignment film, and performing a rubbing alignment or optical alignment; secondly, providing an substrate on which an alignment film is coated; finally, arranging the concave grating and the substrate opposed to each other, filling liquid crystal polymer therebetween, performing alignment on the polymer and curing. As a result, the birefringence grating is obtained.
However, one disadvantage of this method is related to the alignment of the liquid crystal polymer. On the one hand, because the inner surface of the concave grating is domelike, it is difficult to rub all the inner surface and to rub uniformly as well; on the other hand, the height of the domelike concave lens is about 50-500 μm, thus the alignment of the liquid crystal molecules in the center portion of the concave lens can not be aligned perfectly. This poor alignment is the most important problem in the birefringence grating of the 3D display technology.